1. Statement of the Technical Field
The invention concerns sensor equipment, specifically, flexible circuits wherein the flexible circuit serves as a substrate for a contact temperature sensor.
2. Description of the Related Art
Temperature sensing devices are well known in the art. For example, thermocouples and thermistors have been used for many years to perform temperature sensing functions. Notwithstanding their widespread use, thermocouples and thermistors are known to suffer from certain limitations. For example, thermocouples are non-linear devices that have a low sensitivity to small temperature changes and are relatively inaccurate. Errors of less than ±1.0° C. are difficult to achieve. A thermocouple's life span depends on the operating temperature, the operating environment, the thermocouple wire size, and the thermocouple insulation type. A thermocouple's accuracy also decreases as a function of time. For example, the heating and cooling of thermocouple wires causes physical and chemical changes to the wires, such as metallurgical structure changes and reactions with oxygen. As a result, the thermocouple's accuracy range becomes more inefficient over time. Thermistors tend to be more accurate than thermocouples, but they have a much more limited temperature range because of their marked non-linearity.
In recent years, various manufacturers have developed integrated circuit temperature sensing devices. Such devices offer a number of advantages as compared to temperature sensing systems that are based on conventional thermocouple or thermistor technology. For example, integrated circuit temperature sensors can be designed to produce either voltage or current output. The also produce a very linear output that can simplify system design.
Notwithstanding the advantages of integrated circuit temperature sensors, they can also create some practical design problems. For example, such design problems can occur when a sensing device is used to measure a case surface temperature of an electronic device, such as a flange mounted transistor.
Temperature sensors can come in various packages useful for mounting the sensor device to a printed circuit board (PCB) or a printed wiring board (PWB). PCBs and PWBs are rigid insulated boards on which interconnected circuits and components are mounted. However, such sensor architectures often do not provide suitable mechanisms for transporting thermal energy to the sensor from the heat source in order to take an accurate temperature measurement. Some types of sensors, such as thermocouples are offered in a bolt on configuration that is well suited for attachment to certain electronic devices, such as a flange mounted transistor. Such configurations can offer good thermal performance, but still suffer from all of the various disadvantages commonly associated with thermocouple devices.
Alternative solutions to the temperature sensing problem include arrangements that attach a thermal conductor to the device which is to be measured. The thermal conductor can be connected to one or more other thermally conductive elements, which are ultimately connected to the temperature sensing device. The thermally conductive elements can be used to transport heat energy from the device undergoing measurement, to the temperature sensing device. While such arrangements have been used in the past, they also have some disadvantages.
For example, such arrangements typically comprise a large number of parts. These parts can include one or more metal studs or plates, and electrical wiring for powering the sensor and communicating measured data. If a board mounted integrated circuit temperature measuring device is used, then an auxiliary printed wiring board can also be required to accommodate the integrated circuit package and pin-outs. Due to the large number of components and associated assembly labor, this sensor architecture is very costly to manufacture. In addition, thermal performance in these arrangements can be compromised because of the rather long thermal conduction path. This can lead to inaccurate or delayed sensing of temperature variations occurring on the device to be measured.
Despite the various configurations known in the art there remains a need for a more accurate, real time temperature sensing system having an improved mechanical connection between a sensor and a heat source. A flexible, miniaturized temperature sensing system is also needed that is cost efficient by minimizing assembly labor and part count.